The present invention relates to the field of pipes for conveying fluids, in particular corrosive fluids, on land or at sea, and more particularly undersea pipes specifically for conveying sea water, and it also relates to pipe connection parts including an internal liner.
More particularly, the invention relates to connecting together two unitary pipe elements having respective internal linings, and still more particularly to elements having a length of 24 meters (m) to 48 m installed on oil fields in deep water, e.g. at depths in the range 2000 m to 3000 m, or even more, from a laying ship fitted with J-lay towers, with the help of a connection part that is not entirely cylindrical, being an element of the pipe bend type, of the T-branch connection type, or indeed of the tapering sleeve type.
More particularly, the present invention relates to a method of covering the inside surface of a steel connection part having an empty inside volume defined by said inside surface, the covering comprising a liner constituted by a layer of substantially uniform thickness of a thermoplastic material, said connection part having at least two open tubular ends suitable for being connected respectively to at least two steel pipe elements that are preferably lined in the same internal.
For a long time, rehabilitating water, gas, and drainage networks has made use of technologies that avoid trenching, i.e. technologies that consist in inserting a tubular liner inside an existing pipe, the liner generally being made of a flexible material such as thermoplastic or thermosetting materials or composite thermosetting materials, said liners either being inserted after being folded up along a longitudinal generator line so as to form a kidney-shaped cross-section and then rounded out merely by raising internal pressure, or else being inserted after being stretched by being put under traction so that the diameter of said sleeve is reduced to a value that is smaller than the inside diameter of said pipe. Under such circumstances, after being put into place, the tension on the liner is released and said liner then returns to its initial diameter and naturally presses against the inside face of said pipe. That mode of insertion is known under the term “swagelining” and it is commonly used for rehabilitating water or gas pipes over unit distances that may be as long as 500 m, or even 1 kilometer (km) in a straight line.
That technology is also implemented when transporting corrosive fluids under high pressure, thus making it possible to use a conventional pressure-withstanding pipe made of carbon steel, that is therefore inexpensive and easy to connect by welding, with the ability to withstand corrosion being provided by the internal liner. This makes it possible to produce unit lengths that may be several hundreds of meters long that need to be connected together while ensuring continuity of the protection against corrosion. Three types of connection are in common use: connection by flanges, by a screw joint, or by a welded joint. When connection is by flanges, it suffices to fold out the liner over the face of the flange, with the flanges, once clamped together, then pinching the liners face to face, and thus providing continuity in the anti-corrosion function. With screw joints, continuity may be provided for example by a ring provided with gaskets that provide sealing relative to each of the upstream and downstream liners. With welded joints, it is appropriate to terminate the liner at a significant distance from the end of the pipe, e.g. lying in the range 100 millimeters (mm) to 200 mm, so that the heating of the steel wall during welding does not damage said liner. The problem that then arises is providing protection against corrosion in the non-lined zone that extends between the end of the liner in pipe N and the end of the liner in the following pipe N+1.
Patent GB-2 218 488 describes the so-called “swagelining” method that consists in stretching a circular pipe of flexible material, referred to below as a “liner”, so as to reduce its diameter to enable it to be inserted in a pipe by being pulled through, with the diameter of said liner at rest being greater than the inside diameter of said pipe. Another way of inserting such a liner is to deform it by folding it so as to obtain a kidney-shaped cross-section that can be inscribed within a circle of diameter that is much smaller thus making insertion possible merely by pulling the folded liner through the steel pipe. Once pulled through, the ends project considerably and naturally return to a substantially circular shape, and it is simple to fit a plug thereto. By pressurizing its inside with compressed air, the liner is caused to return to its circular shape, and it then presses firmly against the inside wall of the steel pipe.
The following patents GB-2 391 547, GB-2 298 256, WO-2004/015321, and WO-2004/011840 describe assembling together two pipe elements with the help of a tubular junction sleeve inserted into non-lined ends of the steel walls of two pipe elements that are to be assembled together, said tubular junction sleeve being made of a material that withstands corrosion.
Non-published application FR 04/11055 (2876773) in the name of the Applicant describes a method of fitting an internal liner to tubular pipe by threading it through, and a method of welding together pipe elements lined in that way, which methods are both mechanically reliable and also simpler and less expensive to perform, in particular when assembly is performed on site from a ship at sea, on pipe elements of length that is short and suitable for being laid from a ship at sea. Such methods and devices for lining and assembling pipe elements require some minimum number of parts for connecting the non-lined ends of the pipe elements for assembly, and they do not require special tools such as crimping tools to be used while assembling together two lined pipe elements. Those methods and devices for lining and assembling pipe elements are designed to make pipes that are suitable for being laid in great depth, and more particularly pipes that are suitable for injecting water, and more specifically for injecting sea water.
The lining methods described in the state of the prior art are not suitable for internally lining a connection part of inside volume that is defined by a surface that is not cylindrical, i.e. a surface that is not constituted by a single cylinder. When it is desired to continue a pipe with a major change in direction, whether to go from the sea bed towards the surface via a connection part constituted by an element in the form of a pipe bend, or to make a branch connection to another pipe with a connection part constituted by an element in the form of a T-branch connection, it is necessary to make use of connection parts that have inside surfaces that are not constituted by a single cylinder only. Similarly, when it is desired to assemble pipe elements having different inside diameters, it is necessary to make use of sleeves of tapering diameter, presenting an inside diameter at one end that corresponds to the diameter of one of the pipe elements, and an inside diameter at the other end that corresponds to the diameter of the other pipe. For such parts having inside surfaces that are not formed essentially by a single cylinder, methods of lining by threading a liner through are unsuitable.
JP 58 067383 describes a method of lining walls of a non-cylindrical inside volume in a junction part having open tubular orifices, in which a hot-melt resin is inserted into said part before said orifices are closed. Said part is then subjected to rotation in multiple directions at high speed while being heated.
In that method, the hot-melt type resin has strong bonding properties on the wall and it is the centrifugal force generated by the rotation that serves to spread the resin over the entire combined inside surface of the part, with heating encouraging bonding of the resin on the surface of the wall. However, that method does not make it possible to obtain a distribution of genuinely uniform thickness over the entire wall of the inside volume of the part, since centrifugal force is necessarily of varying strength, given that it varies with the square of the distance between the place where it is exerted and the axis of rotation of the part, and this applies even when multidirectional rotation is provided.